This application is based on patent applications 2000-054970, 2000-333609, and 2001-023415 filed in Japan, the contents of which are hereby incorporated by references.
1. Field of the Invention
The present invention relates to an optical interconnection module used for optical data transmission and reception such as optical fiber communication.
2. Description of the Related Art
In a conventional optical interconnection module used for optical data communication, an optical semiconductor device such as a semiconductor laser for emitting light and an optical fiber optically interconnected to the laser are held on the same mounting substrate. Conductive patterns or electrodes are formed on the surface of the mounting substrate for supplying electric power to the optical semiconductor device. Furthermore, a V-shaped groove, on which the optical fiber is held, is formed on the mounting substrate. For realizing a desired interconnection efficiency, it is necessary to form the electrode and the V-shaped groove precisely on the mounting substrate so as to face the optical semiconductor device and the optical fiber precisely.
On the other hand, a condenser lens is used for interconnecting the optical semiconductor device and the optical fiber so as to obtain a desired interconnection efficiency. Since the optical semiconductor device and the optical fiber are fixed on the precisely finished mounting substrate, the optical semiconductor device and the optical fiber can be positioned much closer, and the condenser lens can achieve the desired interconnection efficiency.
A configuration of a first conventional optical interconnection module 70, for example, shown in Publication Gazette of Japanese Patent Application Hei 7-63957 is shown in FIG. 19.
As can be seen from FIG. 19, an optical semiconductor device such as semiconductor laser 72 is fixed on a mounting substrate 80, and an optical fiber 82 is fixed on a V-shaped groove 86 to be optically interconnected with the semiconductor laser 72. The mounting substrate 80 is contained in a cavity 74 of a package 71. A narrow groove 81 and a wide groove 75 are formed on a top surface of the package 71. The optical fiber 82 is directly disposed in the narrow groove 81. A portion of the optical fiber 82 disposed in the wide groove 75 is covered by a protection film 83 and a ferrule 78 made of a glass tube. A metal plate 77 is fixed on the top surface of the package 71 for enclosing the cavity 74. A cover 85 is further fixed on the metal plate 77 for closing an upper opening of the cavity 74.
For sealing the cavity 74, glass powder having a low melting point is filled in the narrow groove 81, and the glass powder is locally heated to be melted by irradiation of laser light beam such as CO2 laser. Thus, melted glass seals the gap between the optical fiber 82 and the narrow groove 81.
A second conventional optical interconnection module with respect to the sealed packaging is proposed in Publication Gazette of Japanese Patent Application Hei 10-227953 (not shown in the figure). A gel resin having a refractive index larger than that of air but smaller than that of the optical fiber and optically transparency is filled in the cavity. A portion in which the gel resin is filled is further sealed by another resin having moisture resistance.
On the other hand, it is necessary to maintain a temperature of the optical semiconductor device at low and constant level for stabling the operation of the optical interconnection module by restricting the temperature rise due to the heat generated in the optical semiconductor device and an electronic circuit used for controlling the optical semiconductor device.
A configuration of a third conventional optical interconnection module 50, for example, shown in Publication Gazette of Japanese Patent Application Hei 10-282373 is shown in FIG. 20.
As can be seen from FIG. 20, an optical semiconductor device such as a semiconductor laser 52 is fixed on a first mounting substrate 53, and a driving circuit 54 is fixed on a second mounting substrate 55. The first and second mounting substrates 53 and 55 are respectively contained in the same cavity of a package 51. An optical fiber 56 is optically interconnected with the semiconductor laser 52 by a condenser lens 57. The semiconductor laser 52 is electrically connected to electrodes 58 and 59 formed on the first mounting substrate 53 and the driving circuit 54 on the second mounting substrate 55 by bonding wires 60.
When an electric current flows in the driving circuit 54 for driving and controlling the semiconductor laser 52, the driving circuit 54 is heated by the current flow, and the temperature of the driving circuit 54 increases. Similarly, when the semiconductor laser 52 is driven for emitting a light beam, the semiconductor laser 52 is heated by the energy conversion from electric energy to light energy, and the temperature of the semiconductor laser 52 increases. If the semiconductor laser 52 and the driving circuit 54 are fixed on the same mounting substrate, the temperature of the semiconductor laser 52 becomes much higher due to not only the self-heating but also the heat from the driving circuit 54. When the temperature of the semiconductor laser 52 is risen, a frequency of the oscillated laser light will be varied and the output power will be reduced, so that they will be the cause of troubles of the optical interconnection module. For solving there problems, the mounting substrates are divided into the first mounting substrate 53 on which the semiconductor laser 52 is fixed and the second mounting substrate 55 on which the driving circuit 54 is fixed.
In the above-mentioned first conventional optical interconnection module 70 shown in FIG. 19, the optical fiber 82 and the glass tube 78 are held on the package 71. When the package 71 is formed by lamination of ceramic thin plates, there is a possibility that the center axis of the narrow groove 81 and/or the center axis of the wide groove 75 is/are largely discrepant from the center of the package 71.
Furthermore, the mounting substrate 80, on which the semiconductor laser 72 and the optical fiber 82 are held, is fixed on the bottom of the cavity 74 of the package 71. It, however, is difficult to coincide a center axis of the V-shaped groove 86 on the mounting substrate 80 with the center axis of the narrow groove 81 by basing on an outer shape of the mounting substrate 80. The mounting substrate 80 is generally manufactured by the following method. A plurality of V-shaped grooves 86 are formed at predetermined positions on the same wafer having a size of several inches. Subsequently, each mounting substrate 80 with the V-shaped groove 86 is cut from the wafer by dicing. Since the dicing has a tolerance inevitably, it is difficult to finish the outer shape of the mounting substrate 80 precisely by dicing.
When the optical fiber 82 is fixed on the mounting substrate 80 and the package 71 with a discrepancy between the center axis of the V-shaped groove 86 and the center axis of the narrow groove 81, the optical fiber 82 and the ferrule 78 cannot be fixed linearly. As a result, undesired bent called xe2x80x9cmicro-bendxe2x80x9d occurs in the optical fiber 82. When a circumferential condition of the optical interconnection module is varied, there is a possibility that the optical fiber will rupture at a portion where the micro-bend occurs.
It is not necessarily impossible that the optical fiber 82 and the ferrule 78 are precisely positioned linear in the narrow groove 81 and the wide groove 75 so as to coincide the center axes of the optical fiber 82 and the ferrule 78 with the center axes of the grooves 75 and 81 for preventing the occurrence of the micro-bend. It, however, is necessary to process a surface treatment to the optical fiber 82 to be observed easily, and to prepare a complex and high functional apparatus for precisely positioning the mounting substrate 80 on the package 71. This causes the difficulty of the assembly of the optical interconnection module.
For preventing the occurrence of the micro-bend in the optical fiber 82, it can be considered that the V-shaped groove 86 and the narrow groove 81 to which the optical fiber 82 is fixed and the wide groove 75 to which the ferrule 78 is fixed are formed on the same mounting substrate at the same time. A widths of the V-shaped groove 86 and the narrow groove 81, however, are generally narrower about 140 xcexcm, but a width of the wide groove 75 is much wider about 1500 xcexcm, and a depth of the wide groove 75 is deeper about 600 xcexcm. Thus, the processes for forming these grooves become complex, and the size of the mounting base member becomes larger. This method is not practical.
In the above-mentioned second conventional optical interconnection module, the gel resin is filled in the cavity for increasing tolerance of the optical interconnection. It, however, is not practical, since the interconnection efficiency will be reduced by the existence of the resin. Furthermore, the transparent resin cannot shield the moisture perfectly, so that the moisture intrudes in the inside of the package of the optical interconnection module through a gap between the mounting substrate and the resin or the optical fiber and the resin, or the like.
As a method for forming the package, a transfer molding is conventionally known. It, however, has a problem that a large strain occurs in the inside the optical interconnection module due to the deformation of the package formed by the resin molding. A deformation quantity with respect to Young""s modulus of resin is shown in FIG. 21. In FIG. 21, the deformation quantity is a discrepancy between the optical device and the optical fiber after the deformation when the primary deformation is assumed to be zero before the deformation. As can be seen from FIG. 21, the larger the Young""s modulus become, the larger the deformation quantity become. Generally, the resin which can be used in the transfer molding has a relatively large Young""s modulus of about 20000 N/mm2, so that a very large strain occurs in the vicinity of the optical interconnection portion due to the pressure of the filled resin and the heat in the resin molding. Thus, the optical interconnection characteristic of the optical interconnection module will be largely deteriorated.
In the above-mentioned third conventional optical interconnection module 50 shown in FIG. 20, the mounting substrate is divided into the first mounting substrate 53 on which the semiconductor device 52 is fixed and the second mounting substrate 55 on which the driving circuit 54 is fixed for preventing the trouble caused by the temperature rise. The first and second mounting substrates 53 and 55, however, are contained in the same package 51, so that the heats occurred in the semiconductor laser 52 and in the driving circuit 54 are mutually transmitted between them through the package 51. When the package 51 is formed of a material having a large heat resistance such as an epoxy resin or a glass, the heats generated in the semiconductor laser 52 and in the driving circuit 54 cannot be radiated effectively, so that not only operation of the optical interconnection module becomes unstable, but also the optical interconnection module will be broken by the temperature rise.
Alternatively, when the package 51 is formed of a material having a small heat resistance such as a metal of copper or aluminum or a ceramic of alumina or aluminum nitride, the heats occurred in the semiconductor laser 52 and in the driving circuit 54 are mutually transmitted between them through the package 51 in a short time. Thus, the temperatures of the semiconductor laser 52 and the driving circuit 54 will be risen. When the optical interconnection module 50 is used in a low temperature atmosphere, the temperature rise of the semiconductor laser 52 and the driving circuit 54 causes no problem. However, when the optical interconnection module 50 is used in a high temperature atmosphere, the temperature rise of the semiconductor laser 52 and the driving circuit 54 will cause serious problems.
Furthermore, in the optical interconnection module 50, the semiconductor laser 52 and the driving circuit 54 are respectively fixed on different mounting substrates 53 and 55 disposed at a predetermined distance, so that not only total length of the wiring becomes too long to drive quickly, but also downsizing of the optical interconnection module 50 is difficult.
Still furthermore, the semiconductor laser 52 and the driving circuit 54 are respectively fixed on different mounting substrates 53 and 55, so that the interconnection characteristic of the semiconductor laser 52 and the optical fiber 56 will be varied due to the difference of the thermal expansions in respective portions.
On the other hand, in a secondary mounting for fixing the optical interconnection module on a circuit substrate, lead wires are conventionally soldered between the optical interconnection module and conductive patterns on the circuit substrate for communicating electric signals between the optical interconnection module and an external circuit equipment. By such a conventional mounting method, it is difficult to downsize and to thin the circuit substrate with the optical interconnection module, and it is unsuitable for a high density surface mounting.
Alternatively, it is considered to connect the optical interconnection module directly to the wiring on the circuit substrate by using soldering bumps without using the lead wires. A material of the circuit substrate, however, is generally a resin such as epoxy, and the material of the package of the optical interconnection module is mainly a metal or a ceramic. When the optical interconnection module is fixed on the circuit substrate by the soldering bumps, the circuit substrate will be warped or deformed due to a difference between the thermal expansion coefficients of the materials of the package of the optical interconnection module and the circuit substrate corresponding to the temperature change. The warp of the circuit substrate will cause not only the deterioration of the optical interconnection module, but also the rupture at the connecting point (soldering bump) of the optical interconnection module and the wiring of the circuit substrate. As a result, the electrical connection between the optical interconnection module and the external equipment is broken so that communication system using the optical interconnection module will be failure.
An object of the present invention is to provide an optical interconnection module and a mounting structure thereof by which an optical fiber and an optical semiconductor device can precisely be interconnected so as to realize a reliable interconnection characteristic in a long term.
An optical interconnection module in accordance with the present invention comprises a first mounting base member and a second mounting base member. At least an optical semiconductor device and an optical fiber interconnected to the optical semiconductor device are held on the first mounting base member. The first mounting base member with the optical semiconductor device and the optical fiber is further fixed on the second mounting base member. At least a gap between the optical semiconductor device and an end face of the optical fiber is filled by a first resin having transparency and moisture resistance. Furthermore, a portion filled by the first resin is covered by a second resin having non-transparency.
By such a configuration, the optical fiber and the optical semiconductor device can precisely be interconnected and firmly fixed on the first mounting base member by the first resin. Since the first resin has transparency, the light emitted from the optical semiconductor device can enter into the optical fiber. Since the first resin has moisture resistance, the optical interconnection portion of the optical semiconductor device and the optical fiber can be protected from affect of the moisture by the first resin. Furthermore, since the optical interconnection portion is covered by non-transparent second resin, external light can be shield by the second resin so as not to enter into the optical fiber. As a result, the reliability of the optical interconnection characteristics of the optical module can be increased, and the characteristics can be maintained in a long term.